Various approaches to mutation detection are being investigated. Parental mice are exposed to mutagens such as ethylnitrosourea, and transmissible alterations in F1 progeny are examined. Characteristics include variant enzymes detected by electrophoresis and/or change in activity, abnormalities in the skeleton, and eye defects, e.g., cataracts. Recessive effects will be examined in separate breeding studies beginning with mutagen treated parents crossing the F1 males to untreated females (same strain as used for treatment in the first generation) and finally backcrossing the F2 females to F1 males.